Polymers in particle form with improved properties, for the preparation of thermoplastic moulding materials

ABSTRACT

Polymer powders and thermoplastic moulding materials with improved properties are obtained if graft polymers and/or resins in particle form are used and small amounts of rubber-like polymers are polymerized or graft-polymerized onto their particle surfaces.

The invention relates to polymers in particle form, their preparationand their use as thermoplastics. Polymers in particle form are usuallyprepared by emulsion polymerization; this particularly applies to graftpolymers of resin-forming monomers on rubber. The polymers can beobtained from the polymer emulsions--especially in the case of graftpolymerization--as powders, which can then be processed asthermoplastics to shaped articles, if appropriate after mixing withbrittle resins (such as styrene/acrylonitrile copolymers or polyvinylchloride).

The properties and the quality of the polymer powders used are decisivefor the properties of the final products: the powders must be purifiedand dehydrated sufficiently, easy to handle and readily dispersible inviscous thermoplastic melts.

It has been found that polymer powders and thermoplastic mouldingmaterials with improved properties can be obtained if graft polymersand/or resins in particle form, onto the particle surfaces of whichsmall amounts of rubber-like polymers are polymerized orgraft-polymerized in a particular manner, are used.

The invention thus relates to

(1) resinous polymers in particle form of 90-99% by weight of a corematerial of a homo- or copolymer of resin-forming monomers and 10-1% byweight of rubber-like homo- or copolymers with glass transitiontemperatures of less than 30° C. polymerized onto the surface of theresin particles and

(2) graft polymers in particle form of a core (a), of a diene, olefineand/or alkyl acrylate rubber, of a grafted shell (b), of a homo- orcopolymer of resin-forming monomers and 10-1% by weight, based on thesum of (a) and (b), of a rubber-like homo- or copolymer with glasstransition temperatures of less than 30° C. polymerized onto the surfaceof the graft polymer particles.

Preferred polymers in particule form have a weighted average particlediameter (d₅₀ value) of 0.08 to 1.5 μm, most preferably 0.09-0.6 μm andconsist of 93-99, in particular 96-99% by weight of core material, whichis a homo- such as copolymer of resin-forming monomers in the case ofthe resinous polymers and is the sum of material (a) and (b) in the caseof graft polymers, and of 7-1, in particular 4-1% by weight of rubberpolymerized on, preferably with glass transition temperatures of lessthan 10° C., in particular less than -10° C.

The resinous polymers in the polymers according to the invention arehomo- or copolymers of resin-forming α,β-unsaturated polymerizablemonomers, such as styrene, α-methylstyrene, p-methylstyrene,halogenostyrene, C₁₋₈ -alkyl methacrylates, acrylonitrile,methacrylonitrile, maleimides and vinyl chloride.

The rubber-like homo- or copolymers polymerized on in the polymersaccording to the invention are derived from monomers for the seriescomprising acrylic acid alkyl esters with up to 8 C atoms in the alcoholpart, diene monomers, such as butadiene, isoprene and chloroprene, andcarboxylic acid vinyl esters, in particular from alkyl acrylates, andbutadiene, and can contain, if appropriate, up to 50% by weight, inparticular up to 30% by weight, of comonomers, such as styrene,acrylonitrile or alkyl methacrylate, it being necessary for the rubbercharacter of the polymers polymerized on to be preserved.

These rubber-like polymers are thus polymerized onto the particles, thatis to say physically or chemically bonded to them; polymers in which therubbers polymerized on are not grafted or grafted to only a low degreebut are fixed physically to the particle surfaces are preferred.

If the polymers in particle form according to the invention are graftpolymers of a core (a) and a resin grafted-on shell (b), the core (a)preferably has an average particle diameter (d₅₀) of 0.09-0.5 μm and theweight ratio of core (a) to shell (b) is 10 to 80 to 90 to 20, inparticular 20 to 80 to 80 to 20. The core material (a) is preferablycrosslinked, in particular highly crosslinked, and preferably consistsof a rubber based on dienes, olefines or alkyl acrylates.

The preferred material of the core (a) is a crosslinked rubber of one ormore conjugated dienes, for example polybutadiene, or a copolymer of aconjugated diene with an ethylenically unsaturated monomer, such asStyrene and/or acrylonitrile, and a crosslinked acrylate rubber, inparticular a Crosslinked polymer of acrylic acid alkyl esters, ifappropriate mixed with up to 40% by weight of other vinyl monomers.

The suitable polymerizable acrylic acid esters include C₁ -C₈ -alkylesters, for example methyl, ethyl, butyl, octyl and 2-ethylhexyl esters,halogenoalkyl esters, preferably C₁ -C₈ -halogenoalkyl esters, such aschloroethyl acrylate, and aromatic esters, such as benzyl acrylate andphenethyl acrylate. They can be used individually or as a mixture, andthe mixture should contain at least one alkyl ester. Polyfunctionalmonomers are copolymerized for crosslinking. Examples are: esters ofunsaturated carboxylic acids with a polyol (preferably 2 to 20 carbonatoms in the ester group), such as ethylene glycol dimethyl acrylate,esters of a polyfunctional carboxylic acid with an unsaturated alcohol(preferably 8 to 30 carbon atoms in the ester radical), triallylcyanurate, triallyl isocyanurate and divinyl compounds, such asdivinylbenzene; esters of unsaturated carboxylic acids with unsaturatedalcohols (preferably 6 to 12 carbon atoms in the ester radical), such asallyl methacrylate; and phosphoric acid esters, for example triallylphosphate, and 1,3,5-triacryloylhexahydro-s-triazine. Particularlypreferred polyfunctional monomers are triallyl cyanurate, triallylisocyanurate, triallyl phosphate, allyl methacrylate, ethylene glycoldimethacrylate and 1,3,5-triacrylloylhexahydro-s-triazine.

The grafted-on shell (b) is derived from the resin-forming monomersmentioned; this resin grafted-on shell (b) is thus at least partlygrafted onto the core (a).

The invention furthermore relates to the use of the polymers in particleform, if appropriate as a mixture with brittle thermoplastic resins, asa thermoplastic moulding material: examples of suitable brittle resinsare polyvinyl chloride, styrene/acrylonitrile copolymer, polystyrene andpolymethyl methacrylate or α-methylstyrene/acrylonitrile copolymers orterpolymers.

The polymers in particle form according to the invention can be employedin the form of powders to prepare these thermoplastic mouldingmaterials: such a powder is usually melted together with thethermoplastic resin and this mixture is then processed by thermoplasticmethods. It is also possible to mix the emulsion of the polymers inparticle form according to the invention with suitable emulsions ordispersions of the brittle thermoplastic resins (for examplestyrene/acrylonitrile copolymer), to precipitate the components togetherand then to use them directly for thermoplastic processing.

The invention furthermore relates to a process for the preparation ofthe polymers and graft polymers in particle form; in which (1)resin-forming monomers are homo- or copolymerized or graft-polymerizedonto a rubber from the series of diene, olefine and/or alkyl acrylatepolymers in aqueous emulsion by polymerization initiated by freeradicals, (2) after a polymerization conversion, based on the sum of theresin-forming monomers, of more than 90% by weight, a monomer or amonomer mixture which results in a rubber-like homo- or copolymer withglass transition temperatures of less than 30° C. is added in an amountof 1-10% by weight, based on the total reaction mixture, and (3) thesemonomers are polymerized on by free radical polymerization.

In the first stage of the process, resin-forming monomers are thuspolymerized or graft-copolymerized in the conventional manner; thisprocess is carried out in an aqueous emulsion, the resin-formingmonomers being graft-copolymerized in the presence of one of the rubbersmentioned in the case of graft polymerization. These emulsionpolymerizations can be carried out batchwise or continuously, usingemulsifiers, regulating additives and polymerization initiators, inparticular water-soluble initiators, at temperatures of 20°-100° C. andpH values of 12-2. A relatively large excess of emulsifier shouldthereby be avoided, especially in the final stage of the polymerization.

After a monomer conversion of more than 90%, preferably more than 94%and especially more than 98%, the monomers which form rubber-like homo-or copolymers are added and free radical polymerization is carried out,during which no further emulsifier or regulator should be added butinitiator must be subsequently metered in, if necessary. Polymerizationwithout the addition of further initiators, that is to say merely byaddition of monomers, is preferred.

In this polymerization, the rubber-like polymer formed is fixed to thelatex particle surface of the previously formed polymers, and anyresidual monomers of the polymerization in stage 1 are copolymerized.This fixing can be graft copolymerization or physical addition of therubber-like polymer onto the surface of the previously formed particles.Particularly high quality polymers in the context of the invention areobtained if grafting is suppressed.

After polymerization of the monomers which form the rubber-like homo- orcopolymers, polymers or graft polymers in particle form in the contextof the invention are obtained in latex form (emulsion).

Such emulsions can be worked up after coagulation with acids, salts orbases, low temperature or heat or by spray-drying to powders;coagulation is preferably carried out at temperatures above 50° C. Afterpurification of the coagulates, for example by washing, the moistpolymers are dried to powders with improved properties in the context ofthe invention.

The emulsions, according to the invention, of polymers or graft polymersin particle form or the polymer powders according to the invention canbe used in an outstanding manner for the preparation of thermoplasticmoulding materials. For preparation of these, the polymers according tothe invention can be processed directly as thermoplastics, volatilecomponents being distilled off if appropriate and if appropriate withthe addition of known antioxidants, lubricants, dyestuffs, pigments,flameproofing additives or antistatics or fillers.

On the other hand, mixtures of the polymers according to the inventioncan also be processed.

The polymers can, for example, also be processed as powders with otherthermoplastics which are in the form of, for example, granules orpowders, likewise as a mixture.

The known units, such as screws, extruders, colanders, kneaders andmills, can be used for thermoplastic processing.

Thermoplastic moulding materials which contain polymers according to theinvention are distinguished by a high stability towards heat; animproved processability and improved mechanical properties areadditionally observed.

The emulsions of the polymers in the context of the invention canfurthermore be purified and dehydrated particularly easily duringworking up due to improved purification properties (on washing) andimproved dehydration properties (for example in centrifuges or presses).

The powders obtained have increased bulk densities coupled with improvedfree-flowing properties, a low dust content, a good storage stabilitywithout forming lumps and uniform particle sizes.

EXAMPLES Rubber used as the graft base

A: Aqueous emulsion of a styrene/butadiene copolymer with 35% by weightof copolymerized styrene and a solids content of 30% by weight; averageparticle diameter of the polymer: 0.11 μm (d₅₀ value); gel content ofthe polymer: 89% by weight.

Polymers according to the invention and comparison experiments

I: 1,715 parts by weight of water, 4 parts by weight of the Na salt ofdisproportionated abietic acid and 3 parts by weight of 1N sodiumhydroxide solution are initially introduced into a reactor. Thefollowing monomer mixture is copolymerized at 80° C. by means ofinitiation with a solution of 4 parts by weight of potassiumperoxidesulphate in 140 parts by weight of water: 483 parts by weight ofα-methylstyrene, 777 parts by weight of methyl methacrylate, 140 partsby weight of acrylonitrile and 3.5 parts by weight oftert.-dodecylmercaptan, the following emulsifier solution beingsimultaneously fed into the reactor during the 6-hour metering time forthe monomer mixture: 860 parts by weight of water, 25 parts by weight ofthe Na salt of disproportionated abietic acid and 18 of 1N sodiumhydroxide solution.

After the end of the addition, the mixture is subsequently stirred at89° C. for 4 hours; the monomer conversion is then 98% by weight.

The latex obtained is now further processed as follows:

    ______________________________________                                        I.1 Polymerization is discontinued (comparison)                               I.2 Addition of a mixture of                                                                    28 parts by weight of n-                                                      butyl acrylate                                                                28 parts by weight of styrene                               I.3 Addition of a mixture of                                                                    30 parts by weight of n-                                                      butyl acrylate                                                                26 parts by weight of styrene                               I.4 Addition of a mixture of                                                                    28 parts by weight of n-                                                      butyl acrylate                                                                28 parts by weight of methyl                                                  methacrylate                                                I.5 Addition of a mixture of                                                                    28 parts by weight of ethyl                                                   acrylate                                                                      28 parts by weight of methyl                                                  methacrylate                                                ______________________________________                                    

After the addition of the monomers (1.2 to 1.5), the mixture isafter-polymerized at 80° C. for 2 hours.

After stabilization with 0.8 part by weight of phenolic antitoxidants,the latices are coagulated at 95°-98° C. by means of a 1:1 mixture ofacetic acid an Mg sulphate.

The polymer slurry obtained is washed under constant conditions (untilthe wash water is free from electrolyte) on a laboratory centrifuge (φ30 cm, 1,400 revolutions/minute, charged with 1,400 g of polymer dryweight) and centrifuged dry. The following values result; the bulkdensities are determined after dehydration of the moist polymer materialat 80° C.

    ______________________________________                                               Time until free                                                                         Bulk density of the                                                 from electrolyte                                                                        dry powder (g/l)                                             ______________________________________                                        I.1      3 hours     190                                                      I.2      1 hour      300                                                      I.3      1 hour      290                                                      I.4      1 hour      250                                                      I.5      1 hour      295                                                      ______________________________________                                    

II. 927 parts by weight of latex A and 643 parts of water are initiallyintroduced into a reactor. Initiation is effected at 70° C. by means ofpotassium peroxydisulphate (5 parts by weight). The following streamsare fed into the reactor at 70° C. in the course of 5 hours:

(1) 386 parts by weight of α-methylstyrene, 622 parts by weight ofmethyl methacrylate, 112 parts by weight of acrylonitrile and 1.5 partsby weight of tert.-dodecylmercaptan

(2) 1,430 parts by weight of water, 25 parts by weight of the Na salt ofdisproportionated abietic acid and 20 parts by weight of 1N sodiumhydroxide solution.

After the end of the addition, after-polymerization is carried out at70° C. for 5 hours. The monomer conversion is 97%. Various batches arethen after-treated as follows:

    ______________________________________                                        II.1    Polymerization is discontinued (comparison)                           II.2    Addition of a mixture of                                                      32 parts by weight of n-butyl acrylate                                        24 parts by weight of styrene                                         II.3    Addition of                                                                   56 parts by weight of ethyl acrylate                                  III.4   Addition of                                                                   56 parts by weight of ethylhexyl acrylate                             III.5   Addition of                                                                   28 parts by weight of ethylhexyl acrylate                                     28 parts by weight of styrene                                         ______________________________________                                        After addition of the monomers (II.2 to II.5), the                            subsequent procedure is as in Examples I.2 to I.5. The                        following data result:                                                        ______________________________________                                                            Residual moisture                                               Time until free                                                                             after        Bulk density                                       from electrolyte                                                                            centrifuging dry                                                                           (g/e)                                        ______________________________________                                        ______________________________________                                        II.1  1.5 hours     72% by weight                                                                              280                                          II.2  0.5 hour      59% by weight                                                                              350                                          II.3  0.5 hour      60% by weight                                                                              300                                          II.4  0.4 hor       60% by weight                                                                              355                                          ______________________________________                                    

Moulding materials according to the invention and comparison experiments

PVC: PVC bulk polymer (Vestolit M6807 from Chem. Werke Huls), K value ofthe PVC is 68.

III: 50 parts by weight of PVC and 50 parts by weight of polymers II.1to II.5 are compounded on a mill at 105° C. in the course of 10 minutes,using a lubricant (0.2 part of Loxiol G70) and stabilizers (1.5 parts ofIrgastab 17M). Sheets 4 mm thick are then produced from the compound bypressing at 190° C. over a period of 10 minutes.

Another test series is compounded at 181° C. for 30 minutes. The crudecolour of test pieces (sheets) produced therefrom is evaluated visually.

    ______________________________________                                        Compound with                                                                              II.1    II.2    III.3 II.4  II.5                                 Impact strength                                                                            n.b.    n.b.    n.b.  n.b.  n.b.                                 Notched impact                                                                             5.5     7       7.5   7     7                                    strength (kg/m.sup.2)                                                         Distortion point                                                                           94      95      94    95    94                                   Vicat B (°C.)                                                          Heat stability                                                                             +       ++      ++    +     ++                                   comparison.sup.(1)                                                            after compounding                                                             for 10 minutes                                                                after compounding                                                                          -       +       ++    ++    ++                                   for 30 minutes                                                                ______________________________________                                         .sup.(1) ++ no discoloration                                                  + almost no discoloration                                                     clear discoloration                                                           n.b. = not broken                                                        

IV. Properties of the graft polymers as a thermoplastic

Thermoplastic properties of the graft polymers

Graft polymers II.1 to II.5 are processed as thermoplastics at 220° C.with the addition of 0.2 part of Loxiol G70. The injection mouldedarticles have the following characteristics:

    ______________________________________                                        Product          II.1   II.2     II.3 II.4                                    ______________________________________                                        Ball indentation hardness                                                                      98     97       98   97                                      (MPA 30")                                                                     Impact strength (kg/m.sup.2)                                                                   52     70       68   72                                      Vicat B (°C.)                                                                           110    110      110  110                                     MFI value (220° C./10 kg)                                                               14     19       20   20                                      ______________________________________                                    

Appendix to the measurement methods used in the text

d₅₀ values are average particle diameters determined by ultracentrifugemeasurement, in this context see: W. Scholtan et al. Colloids Z.Polymere, 250 (1972), pages 783-796

Ball indentation hardness, determined in accordance with DIN 53 456

Impact strength, determined in accordance with DIN 53 453

Notched impact strength, determined in accordance with DIN 53 453

Heat distortion point, determined in accordance with DIN 53 460

MFI value, determined in accordance with DIN 53 735

What is claimed:
 1. A particulate polymer consisting essentially of 90to 99% by weight of a particulate core having a resin surface selectedfrom a homo- or copolymer of resin forming monomers or a graft polymercomprising(a) a diene, olefin, alkyl acrylate rubber or mixtures thereofcore and (b) a homo- or copolymer of resin-forming monomers shell and 10to 1% by weight of a rubber-like homo- or copolymer, with a glasstransition temperature of less than 30° C., graft polymerized onto theresin surface.
 2. A particulate polymer according to claim 1, whereinthe core is a homo- or copolymer of resin-forming monomers.
 3. Aparticulate polymer according to claim 1, wherein the core is a graftpolymer comprised of(a) a diene, olefin, alkyl acrylate rubber ormixture thereof core and (b) a homo- or copolymer of resin-formingmonomers shell.
 4. A particulate polymer according to claim 1 having anaverage particle diameter (d₅₀ value) of 0.08 to 1.5 μm.
 5. Aparticulate polymer according to claim 1, comprising 93 to 99% by weightof the core and 7 to 1% by weight of the rubber-like homo- or copolymerand having an average particle diameter (d₅₀ value) of 0.09 to 0.6 μm.6. A particulate polymer according to claims 1, 2, 3, 4 or 5, comprising96 to 99% by weight of the core and 4 to 1% by weight of the rubber-likehomo- or copolymer.
 7. A particulate polymer according to claims 1, 2,3, 4 or 5, in which the resin-forming monomers are selected from thegroup consisting of styrene, α-methylstyrene, p-methylstyrene,methacrylic acid alkyl esters, acrylonitrile, methacrylonitrile,maleimide and mixtures thereof.
 8. A particulate polymer according toclaim 1, wherein rubber-forming monomers alkyl acrylate, diene andcarboxylic acid vinyl ester monomers mixed with zero to 50% by weight ofstyrene, acrylonitrile or alkyl methacrylate monomers, based on the sumof rubber-forming monomers, are used to form the rubber-like homo- orcopolymer.
 9. A particulate polymer according to claim 1, wherein therubber-forming monomers are C₁ to C₈ alkyl acrylate, butadiene,isoprene, chloroprene, or mixtures thereof.
 10. A particulate polymeraccording to claim 1, wherein the rubber-forming monomers are mixed withzero to 30% by weight of styrene, acrylonitrile or alkyl methacrylate.11. A free flowing particulate polymer in powder form having a uniformparticle size and consisting essentially of, 90 to 99% by weight of aparticulate core comprising a crosslinked acrylate rubber and 10 to 1%by weight of a rubber-like copolymer, having a glass transitiontemperature of less than 30° C., graft polymerized onto the particulatecore.
 12. A particulate polymer according to claim 11 having an averageparticle diameter (d₅₀ value) of 0.08 to 1.5 μm.
 13. A particulatepolymer according to claim 11, consisting essentially of 93 to 99% byweight of the particulate core and 7 to 1% by weight of the rubber-likecopolymer where the particulate polymer has an average particulediameter (d₅₀ value) of 0.09 to 0.6 m.
 14. A particulate polymeraccording to claims 11, 12 or 13, consisting essentially of 96 to 99% byweight of the particulate core and 4 to 1% by weight of the rubber-likecopolymer.
 15. A particulate polymer according to claims 11, 12 or 13 inwhich the resin-forming monomers are selected from the group consistingof styrene, α-methylstyrene, p-methylstyrene, methacrylic acid alkylester, acrylonitrile, methacrylonitrile, maleimide and mixtures thereof.16. A particulate polymer according to claim 11, wherein the rubber-likecopolymer-forming monomers are alkyl acrylate, diene and carboxylic acidvinyl ester monomers mixed with zero to 50% by weight of styrene,acrylonitrile or alkyl methacrylate monomers, based on the sum ofrubber-like copolymerforming monomers.
 17. A particulate polymeraccording to claim 11, wherein the rubber-like copolymer-formingmonomers are C₁ to C₈ alkyl acrylate, butadiene, isoprene orchloroprene.
 18. A particulate polymer according to claim 11, whereinthe rubber-like copolymer-forming monomers are mixed with zero to 30% byweight of styrene, acrylonitrile or alkyl methacrylate.
 19. A processfor the production of a particulate polymer according to claim 11 inwhich (1)--the cross-linked acrylate rubber is polymerized in aqueousemulsion by polymerization initiated by free radicals, (2)--after apolymerization conversion of more than 90%, based on the sum of themonomers used to form said rubber, monomers which form the rubber-likecopolymer are added and (3)--the rubber-like copolymer-forming monomersare polymerized by free radical polymerization.